A rear hub has to do two opposite things: lock to the cassette or sprockets when you pedal forward, and let go when you coast. A one-way clutch inside the hub does this, and it comes in two main forms: small spring-loaded pawls that click into notches, or a pair of toothed ratchet rings that press face to face. The clutch sits in a freehub body (the part the cassette slides onto) or, on older bikes, in a screw-on freewheel.
Freewheel versus freehub
A freewheel is the coasting mechanism itself. Sheldon Brown’s glossary calls it “The mechanism that makes coasting possible.” The word is used in two senses on bikes, so it helps to keep them apart.
- Thread-on freewheel. The ratchet is built into the sprocket cluster, and the whole unit screws onto standard threads on the hub. Because the threads were standardized, as Brown puts it, “a standardized set of threads to which a standard freewheel / sprocket cluster could be screwed on,” a cluster from one brand fit a hub from another.
- Freehub (cassette hub). The ratchet moves into the hub. Brown’s glossary defines Freehub as a “Shimano trademark for a rear hub in which the freewheel mechanism is built into the hub itself”. His page on freewheels and cassettes notes that “The cassette Freehub incorporates the ratchet mechanism into the hub body.” The sprockets then slide onto splines and are held by a lockring, and Brown says the ratchet mechanism is “still replaceable.”
To tell which you have: Brown’s rule is that on a freewheel, “Extractor splines do not turn when sprockets are spun backwards,” while on a cassette, “Lockring splines turn with sprockets when spun backwards.” If you are shopping for a cassette, our guide to bike gearing covers the ratios.
Why the industry moved the ratchet into the hub
The mechanical argument is about where the axle is supported. Jobst Brandt, in an article hosted by Sheldon Brown, observes that “Common freewheel hubs have not only the highest bending stress but the smallest axle at 10 mm diameter.” He attributes axle failures to “bending loads at the middle of the rear axle that arise from bearing support that is not at the ends of the axle.” Brandt describes the better arrangement as one that “carries its loads on bearings at the ends of the axle for minimum axle stress.” Brandt also lists “Durability of the escapement and its angular backlash” as a factor when comparing designs, which is a reminder that no design wins on every count.
Pawl freehubs
A pawl is, in Brown’s words, “A spring-loaded part that engages a set of teeth when moving in one direction.” The pawl engages the teeth in the driving direction and slides over them in the other direction, which is what lets the wheel coast. Brown adds that “The pawls in a freewheel make a ticking sound when a bicycle coasts”, which is the familiar buzz of a coasting bike.
One practical point follows from the design:
- Engagement is quantized. If the pawls land on teeth at fixed intervals, you may have to rotate the pedals a few degrees before the hub catches. As general mechanics, more teeth shrink that gap, which is the idea behind the higher engagement-point counts described below.
Ratchet-ring freehubs
DT Swiss’s Ratchet System replaces pawls with two toothed rings. The company says the simultaneous engagement of the teeth is why this works well: “This is a result of the simultaneous engagement of the teeth, creating far fewer point loads.” The original version “uses two conical springs to ensure the proper alignment of the ratchets”, while the Ratchet EXP version is described as using “Only one guided spring.”
The same maker’s technology pages describe how its variants differ:
| Variant (DT Swiss) | What the maker says |
|---|---|
| Ratchet System (classic) | Two conical springs keep the ratchets aligned. |
| Ratchet EXP | Fewer parts “because of the integration of the ratchet and the threaded ring”; a single cylindrical spring gives “faster full engagement and thus increases reliability.” |
| Ratchet DEG | “has been designed to deliver a small engagement angle while maintaining a high reliability.” |
| Ratchet LN | “uses the same inner parts as the freehub Ratchet System.” |
On Ratchet EXP, the bearing moves into the threaded ring, which “allows the bearing distance to be maximized” and, per DT Swiss, results in “a 15% improvement in axis stiffness.” That is a manufacturer figure for its own design change, not an independent measurement.
Engagement points and what they mean
Engagement points are the number of teeth around the ring. A full turn is 360 degrees, so 36 teeth means about 10 degrees between engagement positions, and each doubling of the count halves the gap. A retailer listing for a DT Swiss upgrade kit states “Version with 54 engagement points for a degree engagement of 6.6°” and compares it to “the 36-tooth ratchets normally installed.” The same listing warns the kit is “NOT compatible with Star-Ratchet, Ratchet DEG and Ratchet LN!”, only with “All DT Swiss rear hubs with Ratchet EXP freehub system.” The lesson: tooth count is a hub-specific part choice, so confirm the exact hub model and generation before ordering parts.
Servicing and when to stop
DT Swiss says “The plug-in construction of the Ratchet System hubs allows for quick and tool-free maintenance,” and that the EXP’s redesigned end caps make disassembly easier. Follow the maker’s service manual for your exact hub: lubricant and procedure differ between designs. Hub bearings and the axle are structural, so take the wheel to a shop if you notice any of the following:
- The hub slips under load, or pedals spin without driving the wheel.
- Play or rumbling in the bearings, or a bent or cracked axle.
- Metal debris inside, or a cassette that wobbles on the body.
Do not ride a wheel that slips under load: sudden loss of drive can throw you off the pedals. Wheel truing is a separate job; see how to true a bicycle wheel, and for chain wear that mimics a slipping hub, chain maintenance.
Sources
- Sheldon Brown: Bicycle Glossary E – F
- Sheldon Brown: Bicycle Glossary P
- Sheldon Brown: Freewheel or Cassette?
- Sheldon Brown (Jobst Brandt): Cassette or Freewheel Hubs
- DT Swiss: Ratchet Technologies Overview
- DT Swiss: Ratchet EXP Technology
- DT Swiss: Ratchet Technology
- ROSE Bikes: DT Swiss upgrade kit 54 teeth for Ratchet EXP
Last reviewed: October 2026.